1. Field of the Invention
The present invention relates to a computerized electro-oculographic system and, more particularly, an integrated system for automated administration of electro-oculographic tests and visual evoked response tests to a patient, and automated processing of results derived from such tests, coupled with use of the processed test results for feedback control of the test stimuli. Automated administration of the tests is conducted either under the direct control of the test administrator via an operator control section (console), or under the automated control of a programmed computer with indirect control by the test administrator.
2. Description of the Prior Art
For a number of years, electro-oculographic (or electro-nystagmographic) techniques have been utilized by physicians to gain useful information about a patient with certain complaints--notably, complaints of disturbed equilibrium. Such information has typically been gained by observing the patient's eye movements during certain kinds of visual and vestibular stimulation. At times, such observations provide the only physical findings that support a patient's complaint, and they also assist the physician in defining the anatomic location of the patient's disorder. For example, by observing eye movements, the physician is often able to distinguish between a peripheral vestibular disorder and one located within the central nervous system, and is sometimes able to lateralize a peripheral disorder, or to further localize a central nervous system disorder.
In early times, the physician examined eye movements merely by watching the patient's eyes. However, important signs were often missed because the physician could not prevent the patient from fixating, and visual fixation has a powerful suppressive effect on some types of nystagmus. Moreover, certain types of brain lesions and certain drugs impair or abolish the visual suppression effect; this phenomenon cannot be appreciated unless nystagmus is observed both when visual fixation is allowed and when it is denied.
A number of methods were available to overcome the latter disadvantages, but the one best suited to the needs of physicians has been electro-oculography. Electro-oculography has long been widely used for research purposes in psychology and ophthalmology. It has gradually acquired its more familiar name, electro-nystagmography, because of its extensive application to the study of nystagmus (although it is used to record other types of eye movements as well).
Basically, electro-nystagmography (ENG) owes its existence to the fact that the eye is, in effect, a battery, the cornea being a positive pole, the retina being a negative pole, and the potential difference between the two poles being normally at least one millivolt. This electrical potential creates, in the front of the head, an electrical field that changes its orientation as the eyeballs rotate. These electrical changes can be detected by electrodes placed on the skin of a patient, and, when the changes are amplified and used to drive a writing instrument, a trace of the eye position is obtained.
As stated in the Manual of Electro-nystagmography by Barber and Stockwell (St. Louis: The C. V. Mosby Company, 1976), electrodes can be arranged on the skin in a number of ways, but a standard technique for clinical purposes involves placement of two electrodes bitemporally (that is, one on the right temple and the other on the left temple) to monitor horizontal eye position, placement of a second pair of electrodes, one above and the other below one of the eyes, to monitor vertical position of the eyes, and placement of an additional electrode, usually on the forehead, to serve as a ground or reference point. Of course, other arrangements of electrodes can be utilized, as are known in the art (for example, an occipital arrangement).
A significant problem in the prior art, relating to the monitoring of eye movements using such electrode arrangements, results from the necessity, or at least desirability, of maintaining a constant relationship between the center position of the eye and a given value of the measured electrical parameter (for example, zero volts). Typically, sustained use of such electrode arrangements and measuring devices results in the development of an offset voltage. That is, the calibration of the measuring device varies so that a center position of the eye no longer results in a reading of zero volts, but rather results in some finite number of volts (referred to as the offset voltage). This has obvious disadvantages with respect to the accuracy of the eye movement measurements.
Inasmuch as such electrode measurement devices are usually equipped with an amplifying stage (or preamplifiers, as the case may be), prior art techniques for zero-adjusting, or biasing, the amplifier arrangement so as to eliminate the offset voltage have been limited to manual techniques. Whereas such manual techniques have been an improvement, they have two major disadvantages. Firstly, such techniques amount to broad-range (coarse) adjustments, at best, and thus do not achieve the narrow-range (fine) adjustments necessary for maximum accuracy in measurements. Secondly, such manual techniques--even if performed on a regular basis--cannot compare with the additional efficiency achieved by continuous, automatic zero-adjustment to eliminate the offset voltage.
As previously mentioned, the placement of small electrodes on the head of the patient makes it possible to record ocular motility. Specifically, electro-oculograms representing measurement of both horizontal and vertical eye movements--and occipital measurements as well--are recorded with the electrodes fixed to the head of the patient. Thus, eye movements and visual responses from the patient can be recorded as the patient undergoes one or more tests. Typically, a series of six ocular motor, vestibular and response tests are conducted, as follows:
(1) Gaze tests--wherein eye movements are recorded as the patient looks straight ahead, to the right, to the left, up and down, both with the eyes open and closed.
(2) Saccadic tests--wherein eye movements are recorded as the patient follows a jumping light spot.
(3) Tracking tests--wherein eye movements are recorded as the patient follows a uniformly moving light spot.
(4) Optokinetic tests--wherein eye movements are recorded as the patient watches vertical stripes moving at various speeds to the right, and then to the left, the test being performed both with the patient stationary while the image revolves, and with the patient revolving while the image is stationary.
(5) Caloric tests--wherein each ear is irrigated twice, once with air above body temperature and once with air below body temperature, the irrigation affecting the vestibular sensors and producing horizontal nystagmus.
(6) Visual evoked response tests--wherein "vision" is assessed, the integrity of the visual pathways (including the optic nerve, optic chiasm, and posterior visual pathways) being analyzed, and the visual evoked response being recorded between occipital electrodes (positioned contralateral to the eye--i.e., electrodes on the right/left occipital, and electrodes on the right/left ear lobe), as stimulated by a burst of short, high-intensity light pulses, and a reference (ground) electrode (placed on the forehead of the patient).
Whereas it is known in the art to administer such tests, such tests have typically been performed in a piecemeal manner by one or more physicians or attendants, operating with various separate and non-integrated components. For example, one device might be utilized to perform the saccadic test, followed by a period of time during which a second piece of equipment is actuated in order to perform the tracking test, and so forth for the remaining tests. Moreover, one group of equipment (light flasher or light scanning equipment) might be utilized for administration of the saccadic and tracking tests, and then a second group of equipment (an optokinetic device in combination with a rotating chair) might be utilized to perform the optokinetic test. The lack of availability of an integrated system for performing these various tests, with the various and different types of equipment, has resulted in both time inefficiencies in the administration of such tests, and more importantly inaccuracy in the statistical data obtained.
Moreover, data obtained as a result of the above-mentioned tests typically include artifacts caused by electronic noise, eye blinks, random eye movements, poor electrode contact, and so forth. In the typical system, wherein minute voltage changes (as little as several microvolts per degree of eye displacement) are amplified many thousands of times, distortion of the statistics is a very real problem. For example, the previously mentioned "offset voltage" phenomenon encountered in electrode measuring arrangements of the type employed with such systems is a major contributor to statistical inaccuracy.
Finally, in the typical prior art system, wherein electrode-measured data is--after amplification--recorded directly on a recording device, there is always the possibility of inaccuracies resulting from either the generation of extraneous signals or improper calibration of the recording equipment. As a result, raw data--no matter how accurately measured and obtained--can be distorted by such extraneous signals and/or inherent lack of calibration of the recording equipment, and the actual data--once erroneously recorded--is irretrievable and lost forever.
There has been some attempt in the prior art to overcome the latter disadvantages. In particular, there have evolved systems--such as that disclosed by Robert W. Baloh et al in "Algorithm for Analyses of Saccadic Eye Movements Using a Digital Computer," Aviation, Space and Environmental Medicine (May 1976), pp. 523 ff.--wherein measured data corresponding to horizontal and vertical eye movements, and target position, are--after digitization--recorded on magnetic tape. Then, at a later time, such digitized records are read into a computer equipped with a Saccade Analysis Program (SAP) developed to analyze, in an off-line mode of operation, the saccadic eye movements previously recorded. Such systems can be equipped with not only a processor and memory, but also various peripheral units (disk drive, magnetic tape drive, graphics display terminal, and hard copy printer).
Whereas such systems display the raw data for visual inspection and allow the user to study the data for possible errors in recording and/or digitization, it is important to note that such systems are nevertheless "off-line" systems whereby data is recorded in one operation and then processed in a second operation (on different equipment) separated by a time lapse there-between.
Another type of prior art system is that exemplified by the disclosure of a "Method and Apparatus for Brain Waveform Examination" in U.S. Pat. No. 3,893,450--Ertl, issued on July 8, 1975. That patent discloses a method and apparatus for examining the brain waveform of a subject (for example, by electro-encephalographic (EEG) techniques) by providing a stimuli (such as light), and determining a characteristic of a mathematically determinable point in the brain waveforms of the subject (for example, by means of an EEG amplifier, filter, zero-crossing detector and computer). Upon making of such determination, the stimulation of the subject by a single photo-stimulator is controlled or varied via a closed-loop feedback path (between, for example, the computer and the single photo-stimulator). However, systems such as are represented by the latter patent do not provide a solution to most, if not all, of the problems discussed above. Thus, the system of the latter patent--even though it provides for immediate processing of the brain waveform data, and resultant control of the single photo-stimulator in accordance therewith--does not comprise an integrated system capable of automated administration of various test stimuli to a patient via employment of an operator control section (console), does not provide for correction of the "offset voltage" phenomenon, does not expressly provide for automated processing of resultant test data so as to provide critical information to the attending physician or test administrator in acceptable format and in a very short period of time, and does not provide for feedback control of various test stimuli in accordance with the automated processing of the test data.
In summary, there has been a need in the prior art for an integrated electro-oculographic system which not only provides for automated test administration (including control of test stimuli) to a patient, and is capable of immediate recording and display of the raw data in real time, followed by rapid and accurate analysis of such raw data so as to provide the attendant or physician with critical information in an acceptable form and in a very short period of time, but also is capable of feedback control of various test stimuli in accordance with the automated processing of test data.